Bioresorable compositions such as polylactides (PLA) are useful for bone fixation and bone repair and have the advantage of not requiring surgical removal after the bone heals. However, the use of polylactides for bone fixation and bone repair can lead to a variety of undesirable side effects, such as inflammation or allergic reactions.
Many calcium phosphates are excellent candidates for use as bone repair substitutes because of their excellent tissue response and osteooconductivity. Incorporating calcium phosphate ceramics, e.g., hydroxyapatite (HA, Ca10(PO4)6(OH)2), tricalcium phosphate (TCP, Ca3(PO4)2) and tetracalcium phosphate (TTCP, Ca4(PO4)2O), monocalcium phosphate (MCP, Ca(H2PO4)2), dicalcium phosphate (DCP, CaHPO4), amorphous calcium phosphate (ACP, Ca3(PO4)2), octacalcium phosphate (OCP, Ca8H2(PO4)6), carbonate-substituted apatite (CAP, Ca10-x/2(PO4)6-x(CO3)x(OH)2), and fluoroapatite (FAP, Ca10(PO4)6(OH,F)2) into the polymer matrix has been proved to be an effective way to improve the clinical performance.
Combining bioactive calcium phosphates, such as hydroxyapatite (HA), tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), monocalcium phosphate (MCP), dicalcium phosphate (DCP), amorphous calcium phosphate (ACP), octacalcium phosphate (OCP), carbonate-substituted apatite (CAP), fluoroapatite (FAP) and other halogen-substitute apatite (XAP) with PLA yields a composition similar to the composition found in bone and teeth. Polylactide/calcium phosphate composites make an implant more osteoconductive and aides in lessening the side-effect of PLA by neutralizing acidic bio-degraded by-products of PLA. Although HA and TCP can be used to consume acidity, they are not suitable for buffering at pH 7.4 due to the complex phenomenon of dissolution-reprecipitation of the solid phase. Because of the slow dissolution, it generally takes a long time for the composite to degrade.
Polylactide/calcium phosphate composites have the potential of improving clinical bone healing. However, current polylactide/calcium phosphate composites have a significant setback due to its mechanical weakness. Due to the weak interfacial strength between inorganic particulate and PLA matrix, as a result, brittle fracture behavior is observed in this biocomposite system.
The current methods of synthesizing polylactide/calcium phosphate composites mostly consist of direct blending or mixing of the polylactide with calcium phosphate particles. This creates weak interfacial adhesion between PLA (hydrophobic) and calcium phosphate (hydrophilic) moieties along with agglomeration or clumping of calcium phosphate particles.